5-HT	serotonin
AD	Alzheimer’s disease
ADHD	attention deficit hyperactivity disorder
ADT	arogenate dehydratase
ANS	autonomic nervous system
APOE	apolipoprotein E
APP	amyloid precursor protein
ASD	autism spectrum disorder
Aβ	amyloid-beta
BBB	blood–brain barrier
BD	bipolar disorder
BDNF	brain-derived neurotrophic factor
CNS	central nervous system
CREB	cAMP response element-binding protein
CRP	C-reactive protein
DA	dopamine
EEC	enteroendocrine cell
ENS	enteric nervous system
FMT	faecal microbiota transplant
GABA	gamma-Aminobutyric acid
GF	germ-free
GFAP	glial fibrillary acidic protein
GI	gastrointestinal
GLP1	glucagon-like peptide-1
GOGAT	oxoglutarate aminotransferase
GPCR	G-protein-coupled receptor
HDAC	histone deacetylase
HPA-axis	hypothalamic-pituitary-adrenal axis
HPHPA	3-(3-hydroxyphenyl)-3-hydroxypropionic acid
IFN-γ	Interferon gamma
IL	interleukin
LBP	lipopolysaccharide binding protein
LDA	linear discriminant analysis
LPS	lipopolysaccharide
MDD	major depressive disorder
MGBA	Microbiota–Gut–Brain Axis
NE	noradrenaline
NFTs	neurofibrillary tangles
PAMP	pathogen-associated molecular pattern
p-cresol	para-cresol
PD	Parkinson’s Disease
PET	positron emission tomography
PYY	peptide YY
REM-sleep	rapid eye movement sleep
sAD	sporadic Alzheimer’s disease
sCD14	soluble cluster of differentiation 14
SCFA	short-chain fatty acid
SCZ	schizophrenia
TGF-β	transforming growth factor beta
TLR	Toll-like receptor
TNF-α	tumour necrosis factor alpha